With the continuous development of advancing communications technologies, the communications system is required to have an increasingly higher access speed. Thus, the Broadband Wireless Access (BWA) communications system is attracting increasing attention. The wireless communications theory shows that the higher a transmitting frequency is, the faster radio waves attenuate over the distance will be. The 802.16e-compliant communications system provides a relatively high working frequency, so its Base Station (BS) has a limited coverage. Therefore, members of the IEEE802 relay working team are setting a standard for multi-hop wireless relay communications system that supports 802.16e Mobile Station (MS) and communicates with BS through one or more Relay Stations (RSs).
FIG. 1 shows a flowchart of MS handover process triggered by MS in the prior art. The process includes the following steps:
Step S101: An MS scans one or more neighboring BSs and obtains the information about the neighboring BS, for example, relative time delay, receive signal strength indicator (RSSI), and carrier-to-interference-and-noise ratio (CINR). Optionally, if the MS performs a correlative scan on the neighboring BS, it is possible to estimate the effective time range of the channel parameters obtained by the MS. The MS reports such information and other scanned information to the serving BS through a scanning result report message (MOB_SCN_REP).
Step S102: The MS sends an MS Handover Request message (MOB_MSHO_REQ) to the serving BS and indicates one or more target BSs and other information to the serving BS, where said one or more target BSs are target BSs that the MS requests handover to.
Step S103: The serving BS determines to negotiate with one or more neighboring BSs regarding the handover information according to the information from the MS and related information about its own maintenance, such as MS UL PHY quality information.
Step S104: The serving BS negotiates, through a backbone network, with each neighboring BS determined in step S103, regarding the handover information. Specifically, the information that the serving BS may provide to the backbone network includes: network access information such as MS authentication, key and basic capacity, PHY quality information between the MS and the serving BS, PHY quality information between the MS and neighboring BS, and related information about MS current service flow and relevant QoS information; the information that the neighboring BS may provide to the backbone network includes: QoS information which may support each MS service flow, service level forecast, HO optimization information and time information for the MS to perform special ranging.
Step S105: According to the MS information from the backbone network and information about BS's own maintenance, the serving BS will take one or more neighboring BSs as target BS(s) which is recommended to MS, and ascertain other handover-related information.
Step S106: The serving BS sends a BS Handover Response message (MOB_BSHO-RSP) to the MS and indicates to the MS the target BS and other handover-related information ascertained in step S105.
Step S107: The MS sends a Handover Indication message (MOB_HO-IND) to the serving BS and indicates to the serving BS the target BS (there is only one target BS) and other handover-related information ascertained by the MS.
Step S108: The MS performs handover in the target BS; simultaneously, the serving BS exchanges information with the target BS through the backbone network to support MS handover.
FIG. 2 shows a flowchart of MS handover process triggered by BS in the prior art. The process includes the following steps:
Step S201: An MS scans one or more neighboring BSs and obtains the information relating to neighboring BS, for example, relative time delay, RSSI, and CINR. Optionally, if the MS performs a correlative scan on the neighboring BS, it is possible to estimate the effective time range that the channel parameters obtained by the MS. The MS reports such information and other scanned relative information to the serving BS through MOB_SCN_REP.
Step S202: The serving BS determines to negotiate with one or more neighboring BSs regarding the handover information according to the information from the MS and information about its own maintenance, such as MS UL PHY quality information.
Step S203: The serving BS negotiates with each neighboring BS determined in step S202 regarding the handover information through a backbone network. Specifically, the information that the serving BS may provide to the backbone network includes: network access information such as MS authentication, key and basic capacity, PHY quality information between the MS and the serving BS, PHY quality information between the MS and neighboring BS, and information about MS current service flow and relevant QoS information; the information that the neighboring BS may provide to the backbone network includes: QoS information which may support each MS service flow, service level forecast, HO optimization information, and time information for providing the MS with special ranging opportunity.
Step S204: According to the MS information from the backbone network and information about BS's own maintenance, the serving BS will take one or more neighboring BSs as target BS(s) which is recommended to MS and ascertains other handover-related information.
Step S205: The serving BS sends MOB_BSHO-REQ to the MS and indicates to the MS the target BS and other handover-related information ascertained in step S204.
Step S206: The MS sends MOB_HO-IND to the serving BS and indicates to the serving BS the target BS (there is only one target BS) and other handover-related information ascertained by the MS.
Step S207: The MS performs handover in the target BS; simultaneously, the serving BS exchanges information with the target BS through the backbone network to support MS handover.
FIG. 3 shows a typical MS handover process with nontransparent RS in the prior art. In the MR network, the nontransparent RS has the same tag type and unique tag as the MR-BS, broadcasting pilot carrier and control signaling (such as MAP signaling). For the MS, the nontransparent RS is a BS, where both RS#2 and RS#3 are nontransparent RSs.
The serving MR-BS exchanges information with the neighboring MR-BS through the backbone network; the serving MR-BS is the service base station of MS and RS#2; the neighboring MR-BS is the service base station of RS#3. For the MS, the serving MR-BS is MS's service base station and RS#2 and RS#3 are MS's neighboring base station.
FIG. 4 shows a flowchart of a handover process triggered by the MS in the prior art. The process includes the following steps:
Step S401: The MS sends MOB_SCN_REP to the serving MR-BS to report the DL PHY quality information of RS#2 and RS#3 (for example, DL RSSI average).
Step S402: The MS sends MOB_MSHO-REQ to the serving MR-BS and indicates one or more potential target stations that the MS requests handover to and other information.
Step S403: The serving MR-BS determines whether to take RS#2 as the potential target station recommended for MS handover based on the MS information and other maintenance information, and determines whether to take RS#3 as the potential target station recommended for MS handover.
Step S404: The serving MR-BS ascertains all the potential target stations recommended to the MS and related information.
Step S405: The serving M R-BS sends MOB-BSHO-RSP to the MS and indicates to the MS one or more potential target stations recommended and related information.
Step S406: The MS sends MOB_HO-IND to the serving MR-BS and indicates the handover target station (only one) and related information ascertained by the MS. If the ascertained handover target station is RS#2, the MS performs handover to RS#2 after sending MOB-HO-IND. If the MS performs general handover (initial ranging is intended for competition) on RS#2, RS#2 may exchange information with the serving MR-BS through an air interface if necessary, to support MS handover. If the MS performs fast handover (initial ranging is intended for a special purpose) on RS#2, before the MS performs handover, the serving MR-BS may instruct, through an air interface, RS#2 to allocate the MS the ranging opportunity.
If the ascertained handover target station is RS#3, the MS performs the operation of handover to RS#3 after sending MOB_HO-IND. If the MS performs general handover (initial ranging is intended for competition) on RS#3, RS#3 may exchange information with the neighboring MR-BS through an air interface if necessary, to support MS handover. If the MS performs fast handover (initial ranging is intended for a special purpose) on RS#3, before the MS performs handover, the serving MR-BS may instruct, through an air interface, RS#3 to allocate the MS the ranging opportunity. At the same time, the serving MR-BS may exchange information with the neighboring MR-BS through the backbone network to support MS handover.
FIG. 5 shows a flowchart of a handover process triggered by the MR-BS in the prior art. The process includes the following steps:
Step S501: The MS sends MOB_SCN_REP to the serving MR-BS to report the DL PHY quality information of RS#2 and RS#3 (for example, DL RSSI average).
Step S502: The serving MR-BS determines whether to take RS#2 as the potential target station recommended for MS handover based on the MS information and other maintenance information, and determines whether to take RS#3 as the potential target station recommended for MS handover.
Step S503: The serving MR-BS ascertains all the potential target stations recommended to the MS and related information.
Step S504: The serving MR-BS sends MOB-BSHO-REQ to the MS and indicates to the MS one or more potential target stations recommended and related information.
Step S505: The MS sends MOB_HO-IND to the serving MR-BS and indicates the handover target station (there is only one target station) and related information ascertained by the MS.
If the ascertained handover target station is RS#2, the MS performs the operation of handover to RS#2 after sending MOB-HO-IND. If the MS performs general handover (initial ranging is intended for competition) on RS#2, RS#2 may exchange information with the serving MR-BS through an air interface if necessary, to support MS handover. If the MS performs fast handover (initial ranging is intended for a special purpose) on RS#2, before the MS performs handover, the serving MR-BS may instruct, through an air interface, RS#2 to allocate the MS the ranging opportunity.
If the ascertained handover target station is RS#3, the MS performs the operation of handover to RS#3 after sending MOB_HO-IND. If the MS performs general handover (initial ranging is intended for competition) on RS#3, RS#3 may exchange information with the neighboring MR-BS through an air interface if necessary, to support MS handover. If the MS performs fast handover (initial ranging is intended for a special purpose) on RS#3, before the MS performs handover, the serving MR-BS may instruct, through an air interface, RS#3 to allocate the MS the ranging opportunity. At the same time, the serving MR-BS may exchange information with the neighboring MR-BS through the backbone network to support MS handover.
Serving stations of the MS may be a nontransparent RS served by the serving MR-BS. Assuming that RS#1, MS handover is performed as shown in FIG. 6 and both the MS and the serving MR-BS may trigger an MS handover request. If the MS triggers the handover request, RS#1 will forward the handover request of the MS to the serving MR-BS, forward the handover response of the serving MR-BS to the MS, and then forward MS handover indication to the serving MR-BS. If the serving MR-BS triggers the handover request, RS#1 will forward the handover request of the serving MR-BS to the MS and forward the MS handover indication to the serving MR-BS. Other processes are the same as the above two processes.
FIG. 7 shows a flowchart of a process of handover to RS#2 through RS#1 and the serving MR-BS triggered by the MS in the prior art. The process includes the following steps:
Step S701: The MS sends MOB-SCN REP to RS#1, including DL RSSI of RS#2 detected by the MS and other scanned information.
Step S702: RS#1 forwards MOB_SCN-REP to the serving MR-BS.
Step S703: The MS sends MOB_MSHO-REQ to RS#1, including the tag of potential target station that the MS requests handover to and related information.
Step S704: RS#1 forwards MOB_MSHO-REQ to the serving MR-BS.
Step S705: The serving MR-BS determines whether to take RS#2 as the potential target station recommended for MS handover based on MS information and other maintenance information.
Step S706: The serving MR-BS ascertains all the potential target stations recommended to the MS and related information.
Step S707: The serving MR-BS sends MOB_BSHO-RSP to RS#1, including the tag list of the potential target stations recommended to the MS by the serving MR-BS and related information.
Step S708: RS#1 forwards MOB_BSHO-RSP to the MS.
Step S709: The MS sends MOB_HO-IND to RS#1, including the tag of the handover target station and related information ascertained by the MS.
Step S710: RS#1 forwards MOB_HO-IND to the MS.
If the ascertained handover target station is RS#2, the MS performs the operation of handover to RS#2 after sending MOB-HO-ND. If the MS performs general handover (initial ranging is intended for competition) on RS#2, RS#2 may exchange information with the serving MR-BS through an air interface if necessary, to support MS handover. If the MS performs fast handover (initial ranging is intended for a special purpose) on RS#2, before the MS performs handover, the serving MR-BS may instruct, through an air interface, RS#2 to allocate the MS the ranging opportunity.
In the process of implementing the embodiments of the present invention, the inventor found that the prior art has at least the following problems: If the neighboring RS of the MS is located in the serving MR cell (RS#2) or the neighboring MR cell (RS#3), the basic information is incomplete, based on which the serving MR-BS of the RS determines whether the RS is suitable for serving as the potential target station of the MS. For example, the failure of the MR-BS of the RS to obtain the current PHY service quality information from subsidiary stations at the RS or obtain the channel quality information between the MS and the target stations detected by the RS may cause inaccurate information to be carried in MOB_BSHO-REQ/RSP sent by the MR-BS of the MS to the MS, which may finally degrade the handover performance of the MS, such as lengthy handover time delay or handover failure.